Patents exist describing devices for dispensing volatile substances in the air through diffusion phenomenon. For instance, U.S. Pat. No. 3,685,734 to Paciorek et al. (Aug. 22, 1972) describes a multi-layer polymeric controlled fragrance-release device. The Paciorek et al. device uses a separate flexible sheet to cover a fragrance bearing middle sheet of plastisol. This cover sheet has very low vapor transmission, but upon its removal, fragrance is reportedly immediately detectable and is gradually released from the device.
U.S. Pat. No. 4,145,001 to Weyenberg et al. (Mar. 20, 1979) also describes a multi-layer polymeric package for the controlled release of a volatile substance (e.g. deodorizer) sandwiched between layers. The outer layers of the laminate are impermeable to the volatile substance and its vapors and thus prevent escape of vapors as long as the package is sealed. Upon opening the package, delamination occurs at the interface between two selected layers such that the volatile substance is covered only on one side by a layer which is permeable to vapors thereby allowing controlled release of volatile materials.
U.S. Pat. No. 5,242,111 to Nakoneczny et al. (Sep. 7, 1993) describes a liquid dispensing device which consists of a sealed flexible bag or pouch containing the supply of the active volatile fluid, a wick located inside a tubular chamber and an emanator which diffuses the liquid. U.S. Pat. No. 5,437,410 to Babasade (Aug. 1, 1995) also describes the use of a wick to dispense a fragrance.
U.S. Pat. No. 4,849,606 to Martens, III et al. (Jul. 18, 1989) describes a tamper-resistant plastic container which has a multi-layered flexible seal over its open end. The container has at least one free standing grid which prevents downward pressure or squeezing of the container's seal which might rupture the seal or result in a leakage of the fluid.
U.S. Pat. No. 5,478,505 to McElfresh et al. (Dec. 26, 1995) describes a device for dispensing fragrance into the atmosphere. This device has an attachment clip and uses low density polyethylene as a diffusion membrane. This membrane is sealed to a plastic container similarly to U.S. Pat. No. 4,849,606 to Martens, III et al.
Similar devices for dispensing pesticides or pest repellants are believed to exist.
Unfortunately, in use, the prior art devices do not generally display a constant release rate from the device over time. At first, the release rate is adequate and steady, but after time, the release rate diminishes, which is not suitable for certain applications wherein a constant release rate over time is desired. Also, the fluid utilization with the prior art devices is generally less than adequate in that even though the device is used up from a practical point of view, fluid still remains in the device which is unutilized, and needs to be disposed of properly.